The body of a neighbour, Genevieve Erin, 50, was also found in their home where she had fled for shelter.

A total of 42 houses were destroyed, 34 of them in Ferny Creek, and another 45 damaged, leaving a repair bill of $6.5 million.

Despite extensive investigations, police have been unable to locate anyone responsible for the fatal fires.

The Arson and Explosive Squad is now looking at the fire with fresh eyes and hope a $1 million reward will help bring anyone with information forward.

"By making a renewed appeal to the public and finding the person responsible for such senseless devastation, we are hoping to provide the families of the victims with some answers," Arson Squad Inspector Michael Roberts said.

A reward of up to $1 million will be paid for information leading to the apprehension and subsequent conviction of the person or persons responsible for the suspicious fires.